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Old 08-27-2015, 05:26 PM   #1
mustafaluigi
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Member#: 354986
Join Date: Apr 2013
Location: Blacksburg, VA
Vehicle:
2013 WRX
Crystal Black Silica

Default Switched Power on Unlock

I was wondering if there was a source of power that would switch on when the vehicle was unlocked with the keyfob. I use an AppRadio with a Miracast Device and would like the MiraCast to boot up sooner so I can get connected faster. If I had a source that would turn on when the vehicle was unlocked and stayed on while driving that would be great. If it timed out after X amount of minutes that would be better but then I'd be asking a bit much.
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Old 08-27-2015, 08:32 PM   #2
tomferd
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Member#: 417301
Join Date: Mar 2015
Chapter/Region: NESIC
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2015 WRX
Black

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It would seem there is something telling the rest of your car that you just unlocked it, because the cabin lights will turn on. I'd try tracing that back. Someone here must know where you could tap that signal. But as far as a 12+ line, I am unsure.

Something else to keep in mind, you are hooking up electronics to be on whenever your car is unlocked. It sounds like a really good way to accidentally kill your car if you leave it unattended for long enough. Be careful, make sure you have some sort of redundancy to prevent that.
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Old 08-28-2015, 01:50 AM   #3
fishfangs
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It all depends on how much effort and money you want to put into it.

The way I could see it is to just run off the constant 12V source directly from the battery with a low voltage disconnect to make sure you don't drain the battery all the way. You could then use a switch of some sort that is triggered via the cabin light as tomferd pointed out. The circuitry might get a bit complicated, however.


Another method which would be easier would be to use diodes or other solid state devices and power the head unit with either the cabin light or the switched accessory power (stock config). This way the head unit will be powered as long as the cabin lighting is on, then will switch over to the original power source once the car is started and driving. To do this you will need to find out if the cabin light circuit can support the load of the added head unit.
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Old 08-28-2015, 10:03 AM   #4
mustafaluigi
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Crystal Black Silica

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Quote:
Originally Posted by fishfangs View Post
It all depends on how much effort and money you want to put into it.

The way I could see it is to just run off the constant 12V source directly from the battery with a low voltage disconnect to make sure you don't drain the battery all the way. You could then use a switch of some sort that is triggered via the cabin light as tomferd pointed out. The circuitry might get a bit complicated, however.


Another method which would be easier would be to use diodes or other solid state devices and power the head unit with either the cabin light or the switched accessory power (stock config). This way the head unit will be powered as long as the cabin lighting is on, then will switch over to the original power source once the car is started and driving. To do this you will need to find out if the cabin light circuit can support the load of the added head unit.
Not looking to power the headunit, just the Miracast device. It pulls maybe 500mw. Just trying to get it to boot up before I get in the car. Whatever it does get powered off of also needs to not turn off when cranking the engine.
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Old 08-28-2015, 04:55 PM   #5
LIChuck
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Member#: 266122
Join Date: Dec 2010
Chapter/Region: Tri-State
Location: Patchogue, NY
Vehicle:
2007 WRX Limited
UGM

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Use a relay.

1 Power the relay coil through a diode from the cabin light power. This will turn the relay on when the light goes on.
2. Connect power to the relay coil through a second diode from accessory power, this will keep the relay on when you start the car and the light goes off.
3. Connect constant power to the common relay terminal.
4. Connect your load to the normally open contact (NC).

When you shut the car off and the light goes out, the power to your load turns off.

Done
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Old 08-29-2015, 02:53 AM   #6
fishfangs
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Quote:
Originally Posted by LIChuck View Post
Use a relay.

1 Power the relay coil through a diode from the cabin light power. This will turn the relay on when the light goes on.
2. Connect power to the relay coil through a second diode from accessory power, this will keep the relay on when you start the car and the light goes off.
3. Connect constant power to the common relay terminal.
4. Connect your load to the normally open contact (NC).

When you shut the car off and the light goes out, the power to your load turns off.

Done
This sounds like it would work! In step 4 did you mean NO instead of NC? I'd recommend a low voltage cutout if this is going on constant power, but that's just me being paranoid.

Wouldn't it also work if a diode is on light power, then have a diode on accessory and connect the two to the device without the relay? It takes out the relay and doesn't need constant power to be connected. Sure, if the light goes out before the key is switched the device would shut off, but I'd think that wouldn't be a scenario that happens too often.
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Old 08-29-2015, 07:45 PM   #7
Reezo
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Pac TR7 would be a better way to do it since you can actually program the milsec turn on
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